This invention generally pertains to the storing of materials in rectangular containers and more particularly to means for closing such rectangular containers and storing them efficiently.
The invention is particularly applicable to rectangular drums requiring low leakage rates and will be described with particular reference thereto. However, it will be appreciated that the invention has broader applications such as the storing of non-toxic liquids and solids and may be advantageously employed in other environments and applications.
For many years, a cylindrical metal drum with associated lid has been a common container used for the storage and transportation of materials. Commonly referred to as "55 gallon drums", these containers need to be durable yet inexpensive and able to be securely closed. In recent years, the typical cylindrical design has begun to give way to a rectangular drum with rounded corners. The rectangular drums are more efficient since they can be packed closer together to store more material in the same space as an equivalent number of cylindrical drums.
While the rectangular drums offer space saving advantages, they have proven to be more difficult to securely close. Common closure devices used for circular drums enable tension to be applied uniformly around the top periphery of the drum and associated lid. However, the corners of a rectangular drum and lid tend to prohibit the uniform transmission of closure forces around the edge of the lid and associated container surface. Since containers must pass rigorous drop tests, so called because the drum is dropped from a specified height and then checked for spillage, and because rectangular drums are used for the storage of dangerous materials such as nuclear wastes, an effective means of closing and attaching the lid to an associated rectangular container is needed.
Closure methods for rectangular drums are well known in the prior art. For example, German Patent 1,198,230 issued to Reese discloses a method of uniformly applying tension to the entire periphery of the lid and container edges. A closure ring is shown which utilizes a hook and a lever to grippingly engage the surface of the lid and top surface of the container. The hook means and lever are located on one of the corners of the closure ring.
While this approach or variations of it overcome many of the drawbacks of previous designs, improvements are still desirable and needed. Although the fastening means is correctly placed on the corner of the drum and lid assembly, the tension forces generated in the closure ring are still not uniformly distributed over the periphery of the mating surfaces. It is believed that the corner opposite the lever and hook assembly will receive less tension than the other three corners. Further, the sides of the drum between corners will receive a proportionately lighter load of tension leading to potential spillage problems. Finally, the fastening means wastes valuable space when the drums are stacked together. The lever necessarily extends beyond the surface of the drum preventing the drums from being stacked closely together.
Consequently, a need exists for improvements in rectangular closure mechanisms which will result in more uniform distribution of closure forces over the periphery of the mating surfaces while retaining the storage efficiency inherent in rectangular storage containers.
The present invention provides a closure apparatus designed to satisfy the aforementioned needs.